The present invention relates to thermoplastic polyurethane resins characterized by reduced or eliminated surface haze (blooming).
The phenomenon of "blooming" which is also referred to as "surface haze" in the context of articles molded of polyurethane resins has long been recognized in the art. The degree of blooming and the effectiveness of corrective methods are determined by observation. One technique for determining the degree of blooming is to extrude the polyurethane composition to form a strand and then monitor the surface haze of that strand over a period of several days. The development of haze, the time in which development of the haze occurs and the extent of the haze enable the skilled artisan to distinguish between compositions on the basis of their susceptibility to blooming.
Products such as elastomers, thermoplastically molded articles and textile coatings are known to develop this surface imperfection and means for alleviating this problem have long been sought. The products that are most susceptible to blooming are those composed of polyester polyols, a short chain diol, and MDI (diphenylmethane diisocyanate).